Electric current rectifier



18, s WIDMER ELECTRIC CURRENT RECTIFIER Filed March 31, 1931 inventor Stefan Widmer By Q Attorney Patented Apr. 18, 1933 UNITED STATES PATENT OFFICE STEFAN WIDMER, OF BADEN, SWITZERLAND, ASSIGNOB TO AKTIENGESELLSCEAFT BROWN BOVERI & 0115., OF BADEN, SWITZERLAND, A JOINT-STOCK COMPANY OF SWITZERLAND ELECTRIC CURRENT RECTIFIER Application filed March 31, 1931, Serial No. 526,644, and in Germany April 14, 1930.

This invention relates to improvements in electric power rectifiers and particularly to means for controlling fixation of the point of attachment of an arc flowing therein on the cathode.

Various means have been proposed heretofore for the purpose of fixing the spot at which the arc attaches on the cathode in a metallic vapor arc electric power rectifier to reduce the quantity of cathode material, which is usually mercury, vaporized by movement of the are over the surface of the cathode. Among such means were the provision of fixed pins, strips or other forms of material such as tungsten, or molybdenum or other diflicultly fusible material. It has been found however that such means do not accomplish the desired purpose without attendant disadvantages counter-balancing the improvement in operation of the rectifier due to fixation of the arc.

When a rectifier of the mercury arc type is in operation, fixation of the cathode spot materially reduces the amount of mercury vapor produced relative to the amount of vapor produced by an are moving freely over the cathode surface. Such decrease in the amount of vapor within the rectifier greatly reduces the danger of backfires i. e. flow of current from the cathode to the anode because the fiow of vapor to the anodes is reduced. When a rectifier with the usual control grids is to be started however, the difficulty already present of starting a rectifier with grids is increased due to the fact that fixation of the are at one spot on the cathode does not permit the production of sufficient vapor to allow the ionized vapor to reach the main anode and the transfer of the arc to the main anodes is therefore impossible.

It is, therefore, among the objects of the present invention to provide means for fixing the are in an electric power rectifier of the metallic vapor type which means will permit ready starting of the rectifier.

Another object of the invention is to provide means for fixing the arc in an electric power rectifier of the metallic vapor type which means will be made inoperative during the period of starting of the rectifier.

Another object of the invention is to provide means for fixing the arc in an electric power rectifier of the metallic vapor type in which the fixing means will be raised above the level of the cathode material into operative position after the are has attached to the main anodes of the rectifier.

Another object of the invention is to provide means for fixing the arc in an electric power rectifier of the metallic vapor type in which an arc fixing means and an ignition means are combined to cause ignition of the rectifier and withdrawal of the arc fixing means into inoperative positions by the same movement. I

Objects and advantages, other than those above set forth, will be apparent from the following description when read in connection with the accompanying drawing in which Figure 1 diagrammatically illustrates an electric power rectifier of the metal enclosed metallic vapor arc type embodying one modification of the present invention,

Fig. 2 is a fragmentary view of the rectifier structure shown in Fig. 1 but illustrating an electrically operable modification of an arc fixing means movable into the operative position as desired,

Fig. 3 is a view similar to that shown in Fig. 2 but showing the fixing means controlled automatically in dependence on the rectifier current,

Fig. 4 is a view generally similar to that shown in Fig. 2 but showing a modification of an arc fixing means combined with an ignition means, both means being actuated upon starting of the rectifier,

Fig. 5 is a fragmentary view of a rectifier structure showing means for fixing the are permanently attached to the rectifier cathode plate together with means for raising the level of the cathode material to make the fixing means inoperative, and

Fig. 6 is a view similar to that shown in Fig. 5 but showing a modification of the means to raise the level of the cathode material to make the arc fixing means inoperative when desired.

Referring more particularly to the drawing by characters of reference, the reference numeral 11 designates the metallic housing or tank of an electric power rectifier structure. A plurality of main anodes 12, a plurality of auxiliary or excitation anodes 13 and an ignition anode 14 all extend through the cover of the tank 11 in suitably insulated relation therewith. The main anodes 12 are partially enclosed by sleeves or are guides 16 supported from the insulator bushing through the top of the tank. A grid 17, which may be a grating, a sieve or other apertured member is arranged in each of the are guides as shown and serves to aid in controlling operation of the rectifier as is wellknown. Such grids though advantageous in controlling operation of the rectifier tend to prevent starting thereof as is explained above.

The tank 11 is formed with a bottom substantially in the shape of a frustrum of a hollow cone and a well to receive fluid cathode. material such as mercury shown at 18 is formed by a cylinder 21 of insulating material encircling the aperture in the tank bottom and a bottom plate 22 closing the open bottom of the cylinder 21.

A plate or bar arc fixing member 26 of difficultly fusible material is movably supported above the surface or within the fluid cathode material 18 by means of a rod 27 passing through a suitable sealing gland in the bot tom plate 22 of the cathode well. The rod 27 may be moved to raise or lower the fixing plate 26 by the operation of a lever 28 pivotally connected with rod at 29 and pivotally mounted at 30. The lever 28 may be operated by either mechanical or electrical means such as a solenoid 31 energized from a source of current 32 upon closing of a switch 33. When the rectifier is being started, plate 26 is withdrawn below the level of the cathode mercury 18 thereby permitting ready movement of the arc struck by the ignition anode 14, and transferred to the excitation anodes 13, over the surface of the cathode. Such movement of the arc creates sufiicient quantities of mercury vapor to permit transfer of the arc to the main 'anode. Solenoid 31 is then de-energized and plate 26 rises above the surface of the Cathode material due to its buoyancy in mercury. The are flowing between the anodes and the cathode, in its movement over the cathode. touches and attaches itself to the plate. The heating of the oathode and the quantity of material vaporized from the cathode is thus reduced thereby reducing the danger of backfires. The present movable are fixing means thus permits vaporization of large quantities of material when required and reduces the amount of vaporization when lesser amounts of material are required. I

Figure 2 illustrates a modification of Fig ure 1 in which rod 27 is connected with the operable by con itions in the starting system of the rectifier by means well-known in the art.

Figure 3 shows a structure very similar to that shown in Figure 2 with the exception that the coil 37 is connected across a shunt 41 directly with the direct current output circuit of the rectifier so that the coil is energized sufficiently to cause raising of plate 26 only after the arc has been transferred to the main anodes. Thus when the rectifier current is low, the buoyancy of plate 26 is overcome by spring 45.

Figure 4 shows a combined fixing and ignition means in which the connection between plate 26 and core 36 is hollow and is formed, at its upward end, as a nozzle 41. Cylinder 38 is again in communication with the cathode well and is therefore filled with mercury. Coil 37' is connected through the switch 40 with the battery 39 as before. Core 36 is thus drawn downwardly thereby drawing plate 26 beneath the surface of the mercury as soon as the coil 37 is energized. Downward movement of core 36 forces a jet of mercury against ignition anode 14 whereupon an arc is immediately struck in the ignition ,circuit and is transferred to the excitation anodes. The retraction of the plate and ejection of the mercury are thus substantially simultaneous results of the same switch movement.

Figure 5 shows a stationary fixing plate 46 secured on the bottom plate 22 of the cathode well. A conduit 47 leading from the cathode well is connected through a flexible connection 48 with a sealed reservoir 49 containing mercury. The reservoir 49 may be raised by any suitable means thereby causing discharge of mercury therefrom in such amount as to cover plates 46 entirely during the starting period of the rectifier.

Figure 6 shows a modification of the structure shown in Figure 5 in which the conduit 47 is extended into a reservoir 51 which may be raised and lowered by suitable means such as the Windlass 52 shown to raise or lower the level of the mercury in the cathode well. Conduit 47 may then be made without joints or any flexible portion by which air might be permitted to enter the rectifier.

It will thus be seen that the present invention provides means for fixing the cathode spot in a metallic vapor power rectifier thereby reducing the amount of vapor produced during operation which results in decreased danger of backfiring and that the fixing means may be made inoperative during the starting period of the rectifier thereby facilitating transfer of the arc to the main anodes thereof.

Although but a few embodiments of the' present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from. the scope of the appended claims.

The invention claimed is:

1. In an electric power rectifier structure of the metallic vapor arc type comprising a tank, anodes extending into the tank, and a fluid metallic cathode, the tank having a well formed therein to receive the cathode material; means for maintaining attachment of an arc flowing from the anode to the cathode at a fixed point on the cathode during operation of the rectifier, said means being inoperative to prevent movement of said are over the cathode during starting of the rectifier.

2. In an electric power rectifier structure of the metallic vapor arc type comprising a tank, anodes extending into the tank, and a fluid metallic cathode, the tank having a well formed therein to receive the cathode material; means for fixing the point of attachment of an arc flowing from the anodes to the cathode, said means being movable relative to the surface of the cathode.

3. In an electric power rectifier structure of the metallic vapor arc type comprising a tank, anodes extending into the tank, and a fluid metallic cathode, the tank having a well formed therein toreceive the cathode material; means for fixing the point of atand electro-magnetic means for raising and lowering said plate relative to the surface of said cathode, said means being controlled in response to the direct-current output of the rectifier.

7. In an electric power rectifier structure of the metallic vapor arc type comprising a tank, anodes extending into the tank, and a fluid metallic cathode, the tank having a well formed therein to receive the cathode material; a cylinder fastened on and in com munication with the cathode well, a solenoid core movable within said cylinder, a solenoid coil arranged about said cylinder, and a plate of diflicultly fusible material connected with said core and movable thereby to permit attachment ofthe arc thereon when said coil is deenergized.

8. In an electric power rectifier structure of the metallic vapor arc type comprising a tank, anodes extending into the tank, and a fluid metallic cathode, the tank having a well formed therein to receive the cathode material; a cylinder fastened on and in communication withthe cathode'well, a solenoid core movable within said cylinder, a solenoid coil arranged about said cylinder, and a plate of difficultly fusible material to permit attachment of the arc thereon, and a. hollow connection between said core and said plate to cause movement of both upon energization of said coil, said connection causing ejection of a jet of mercury against .one of the anodes to create an are upon energization of said coil.

In testimony whereof I have hereunto subscribed my name this 19 day of March A. D. i i

STEFAN WIDMER.

into, the cathode to avoid attachment of the arc thereon during starting of the rectifier. 4. In an electric power rectifier structure of the metallic vapor arc type comprising a tank, anodes extending into the tank, and a fluid metallic cathode, the tank havinga well formedtherein to receive the cathode material; a plate of difficultly fusible metal, and means for raising and lowering said plate relative to the surface of the cathode.

5. In an electric power rectifier structure of the metallic vapor arc type comprising a tank, anodes extending into the tank, and a fluid metallic cathode, the tank having a well formed therein to receive the cathode material; a plate of diificultly fusible metal, and electro-magnetic means for raising and lowering said plate relative to the surface of said cathode.

6. In an electric power rectifier structure of the metallic vapor arc type comprising a tank, anodes extending into the tank, and a fluid metallic cathode, the tank having a well formed therein to receive the cathode material; a plate of difiicultly fusible metal, 

